1. Field of the Invention
This invention relates to monitoring drillstring vibration during the drilling of a well.
2. The Prior Art
Drill pipe and bottom hole assemblies in a drillstring experience a wide range of vibration during drilling operations. Excessive vibrations lead to failure of components in the drillstring. This is especially true for the more vibration-sensitive components employed in measuring-while-drilling tools, such as are described in U.S. Pat. No. 4,216,536 to More (1980). Even moderate vibration, when sustained for extended periods of time, can decrease the useful life of relatively rugged components, such as drill bit bearings. Vibration damage increases drilling costs due to loss of rig time, equipment replacement, and, in the worst case, loss of the hole.
For many years, the drilling industry has sought ways to predict, monitor, and control drillstring vibration to avoid partial or catastrophic failure of components in the drillstring. For example, see the Dareing et al paper, entitled "Longitudinal And Angular Drillstring Vibrations With Damping" (ASME Paper 68-Pet- Sept. 30 1968), which presents an analysis of drillstring vibration that included all parts of the drillstrigg from the bit to the elevators. Dareing's later Paper No. SPE 11228, entitled "Drill Collar Length Is A Major Factor In Vibration Control", presented to the Society of Petroleum Engineers of AIME in 1982, emphasizes that the drillstring bottom hole assembly (which includes the drill collars) is the major factor which determines vibration, and suggests equations for calculating critical speeds for various drill collar lengths.
The industry has used critical rotary speed formulae provided in API RP 7G since 1970 to try to prevent unacceptable vibration in the drillstring. However, recent work suggests that rotary speeds which induce vibration in bottom hole assemblies cannot be accurately predicted using the API RP 7G equations.
Wolf et al presented Paper No. SPE 14330, entitled "Field Measurements Of Downhole Drillstring Vibrations", to the Society of Petroleum Engineers in 1985 reporting the use of a downhole sensor string and a hardwire telemetry link (described in Denison's article entitled "Shell's High- Data-Rate Drilling Telemetry System Passes First Field Test", in the June 13, 1977, issue of Oil and Gas Journal, p. 63) through the drillstring to transmit downhole drillstring vibration data to the surface. Although the hardwire telemetry link provides immediate (i.e., real-time) downhole vibration data to the surface, the hardwire system is depth-limited because of its expense, and it disrupts drilling operations as drill pipe sections are added to, or removed from, the drillstring during trips into or out of the well.
Reliable control of bottom hole assembly vibration requires collection and analysis of enormous amounts of field data, which have not been economically available before this invention.